The present invention relates to an implosion prevention band, and particularly to a tension band wherein the width and tension adjusting features of the band are designed to optimize the compressive forces on the faceplate panel of a CRT.
A conventional color CRT includes a radiused glass faceplate panel having a sidewall sealed to a funnel along a planar sealing interface known as a frit seal line. The CRT is evacuated to a very low pressure causing the tube to deform mechanically with resulting stresses produced by the vacuum and by the atmospheric pressure acting on all surfaces of the CRT. Accordingly, such stresses subject the tube to the possibility of implosion as a result of an impact to the glass faceplate panel. Such impact to the glass faceplate panel can cause the panel to shatter into many fragments, projecting the glass fragments in random directions with considerable force.
The most common solution to the implosion problem is to use convexly radiused faceplate panels with increased glass thickness near the edges of the faceplate panel to resist the stresses described above. In conjunction with the curved faceplate panel, it is also known to use an implosion prevention band consisting of a metal tension band around and tightly against the faceplate sidewalls of the CRT so as to exert a radial compressive force to the sidewalls of the faceplate panel. As tension in the implosion protection band is increased, the compressive force on the sidewall also increases causing the faceplate to dome outward in the direction of the viewing surface.
The curvature of the faceplate panel allows for the vacuum forces within the tube to be distributed through the faceplate panel. However, deformation of the tube also introduces tensile stresses throughout the faceplate panel and sidewalls. The tension bands are also used to apply a compressive force to the sidewalls of the CRT to redistribute some of the faceplate panel forces. The redistribution of the faceplate forces decreases the probability of an implosion of the tube by minimizing tensile forces in the sidewalls and corners of the faceplate panel. Implosion prevention bands are also beneficial because they improve the impact resistance of the tube because glass in compression is stronger than glass which is not in compression. Additionally, in the event of an implosion the redistributed stresses cause the imploding glass to be directed toward the back of the cabinet in which the tube is mounted, thereby substantially containing the glass fragments of the imploding tube.
An industry trend is moving towards flatter, less radiused viewing surfaces on the faceplate panel. Unfortunately, the implosion protection techniques that have been used successfully with curved faceplate panel tubes, as described above, have proven inadequate when used with these CRTs having reduced curvature or completely flat faceplate panels. Because of their geometry, the stresses on these flat panels differ from traditional radiused tubes in many ways. For example, high tensile stress areas tend to reside on the surface of the sidewalls. These stress areas continue across the frit seal and into the funnel. Glass defects in these areas become crack sources and result in unacceptable implosion characteristics for the CRT.
Conventional folded tension band systems having an inner overlapping portion of metal folded upon itself along the forward edge of the band have been proposed. However, these bands are difficult to manufacture, and the use of these bands results in a high manufacturing cost. Moreover, tubes using these types of bands having flat faceplate panels, such as in wide screen televisions using a 16:9 aspect ratio, instead of the commoner tubes having the 4:3 aspect ratio, will be subject to additional pressure exerted on the glass along the straight edge of the sidewall with the use of such bands due to the elongated sides of the panel.
The present invention provides a CRT having a substantially flat faceplate panel fastened with an implosion prevention tension band which comprises a single layer band unit surrounding the panel and extending from near the viewing faceplate of the panel to at least half the distance between the rear edge of the inside blend radius and the rear edge of the sidewall of the CRT panel. According to another aspect of the present invention, the tension band includes a plurality of tension adjusting features being positioned at locations around the band aft of the inside blend radius.